What is the best decision you have taken in your life?

Taking medication after getting diagnosed with ADHD. It explained many whys and turned my life around.

Putting a few thousand dollars into a retirement fund in my 20s.

Besides giving me a break on my taxes, my employer also matched the contribution. And then on average a good fund doubles in value about every 10 years. (Do the math -- every $1,000 becomes $2,000, $4,000, $8,000, and then $16,000 before your retire.)

Also, you can tap the money for health emergencies, education expenses, and even first-home purchases.

Hmmm .. as regards IT, early on in your career, learn a skill/programming language that's popular at the time but is solid and popular enough to still be useful when new alternatives come out. For me, I had a 1 week Perl course and then straight into the project. 35 years later I was still writing and maintaining Perl scripts some of which I'd written at the start. Great fun!

Practicing meditation consistently. I understood the power of now. Making reading books a daily habit was also a good decision.

Switching to Linux as a daily driver. Never have to fight against my own computer serving someone else or arbitrarily changing the UX.